In recent years the method or mode of operating fuel burners has been altered because of the escalating cost of fuel. Until recent years, fuel burners, particularly oil burners, were operated with an intermittent source of ignition, a source of combustion air, and the continuous monitoring of a flame by a sensor. The sensor normally was a cadmium sulfide type of cell. The control devices themselves generally were large and utilized electromechanical components.
In order to accommodate for the higher operating costs, fuel burners of the oil burner type are now more commonly operated with an interrupted source of ignition. The quality of the fuel being used now varies considerably, as opposed to a more uniform quality of fuel that was available a number of years ago. This variation in fuel quality and the intermittent operation of an ignition source provides a potential for the loss of flame which is less stable under present operating conditions than under the older operating conditions. Also, the power available to the control devices from the normal line sources has more of a tendency to vary now than the better regulated potentials that were available in the past.
The poor regulation, the variance in fuel, the intermittent ignition, and other related problems tends to create a fuel burner or oil burner environment which is less stable than desirable.